The present invention relates generally to cannulas. More specifically, the present invention relates to cannulas for use in systems for delivering a beneficial agent to a patient or into a system for later delivery to a patient.
Pointed cannulas for use with injection sites have been known for use in the medical arena. Such cannulas can be utilized to access a medicament contained within a container or to create a fluid flow path within a housing. An example of an injection site usable with a piercing cannula is disclosed in U.S. Pat. No. 4,412,573.
Within a housing, to create a fluid flow path, a pointed cannula is utilized that is forced through a septum to create a flow path within the housing. Injection sites, however, which are utilized on a repetitive basis can be damaged by repetitive piercing by a sharp cannula. This damage, known as coring or laceration, can result in a subsequent leakage within the housing. As set forth in detail below, other disadvantages may exist with respect to pointed cannulas when they are used in drug delivery systems.
U.S. Pat. No. 4,537,593 discloses an allegedly non-coring self-venting needle assembly for use in the transfer of liquid to or from a container. The shaft of the needle includes a planar portion terminating in an edge and an aperture aligned with the edge to allow liquid to exit the shaft of the needle.
For many applications, drugs may be mixed with a diluent before being delivered, for example, intravenously, to a patient. The diluent may be, for example, a dextrose solution, a saline solution, or even water. To this end, many drugs are supplied in powder form and packaged in glass vials or ampules. Other drugs, such as chemotherapy drugs, are packaged in glass vials or ampules in a liquid state.
Powdered drugs may be reconstituted by utilizing a syringe to inject liquid into a vial for mixing; the syringe eventually withdrawing the mixed solution from the vial. When a drug must be diluted before delivery to a patient, the drug is often injected into a container of diluent after it is reconstituted, where the container can be connected to an administration set for delivery to the patient.
There are a variety of examples of drug delivery systems. An example of such a system is disclosed in U.S. Pat. No. 4,850,978. The system includes a cartridge for introducing a beneficial agent into a fluid conduit for delivery of the agent to a patient. The cartridge includes a rigid hollow tube and an agent-containing chamber slidably mounted at least partially within the tube. In a first, pre-use, position, the chamber extends farther from the hollow tube than it does in a second position. A cannula is mounted to the hollow tube extending opposite the chamber. When the chamber is in the second position, the cannula pierces a closure means creating a fluid flow path.
U.S. Pat. No. 4,804,366 also discloses a drug delivery system including an adaptor having an improved flow path means providing both an inlet and an outlet to the agent-containing chamber of a cartridge. The cartridge and adaptor permit a single opening through the injection sites at opposite ends of the flow path means, while still permitting simultaneous flow both into and out of the chamber. An adaptor and a cartridge is provided including a rigid cannula with an inlet and an outlet and a shell substantially coaxial and spaced from the cannula intermediate of the cannula inlet and the cannula outlet, so that the shell of the cannula defines a channel therebetween. Both the cannula inlet and the cannula outlet are adaptable to form a single piercing opening in a resilient injection site associated with the receptacle of the delivery system. Both the channel outlet and channel inlet are adapted to form a single piercing opening in a resilient injection site associated with the cartridge.
The two above described systems provide automatic systems for drug delivery and reconstituting a drug. Manual devices that can be used for reconstituting a drug in a vial do not typically have the same concerns that are faced in automatic systems, such as those described above. Typically, in manual systems, the cannula is used to infuse liquid and a separate member is used to vent air as disclosed in U.S. Pat. No. 4,537,593. High pressure and high velocity diluent is passed through the cannula for a short period of time. The vials, after the diluent is injected, are typically manually agitated prior to complete drug dissolution. Pressure differential between the vial contents and the syringe barrel drive the mixture into the syringe. The user can pull a vacuum in the syringe barrel.
A number of concerns and requirements are raised in automatic systems that are not typically present in such manual systems.
Aside from coring problems, a pointed cannula, for being received within a septum in an automatic system that closes a vial containing a powdered drug, may have other disadvantages. When the pointed cannula is inserted into the vial, the powdered drug can be received within the pointed cannula plugging the cannula and preventing fluid flow therethrough. This, however, must be contrasted with the need for an opening that allows the maximum amount of air is displaced as the vial fills. This condition dictates that the cannula opening is located as close as possible to the distal end of the cannula.
In a reconstitution device, fluid passing through the drug bed by means of an inlet and an outlet at opposite ends of the vial erode the drug. Dissolution of the drug is correlated to fluid volume throughput. Due to the low operating system pressure and delivery rates of automatic systems, it is important that restrictions are not created through the outlet of the cannula that impede fluid flow.
A further requirement with respect to drug delivery or reconstitution devices is the need to maintain the integrity of the system. It is therefore important to maintain a closed system during vial inactivation, i.e., when the cannula pierces the septum.
Furthermore, unlike manual reconstitution devices, automatic reconstitution devices require a different set of flow conditions. Partially dissolved clumps of drugs must be restricted from entering the cannula lumen during the dissolution process. If particles enter the lumen this can result in blockage of the lumen and nonuniform drug delivery profiles or complete failure.